That difficulty aside, they were selected because they contain very little uranium and thorium and are therefore unlikely to contain significant radiogenic lead.
Despite this, the momentum gained in the two decades prior to 1972 has made 4.5 b.y.
a popularly accepted “universal constant” even though the foundations on which it was based have been virtually removed.
magazine has been continuously published since 1978, we are publishing some of the articles from the archives for historical interest, such as this.
For teaching and sharing purposes, readers are advised to supplement these historic articles with more up-to-date ones suggested in the Related Articles and Further Reading below.
Some evidence is also presented to show that radiometric results that are in agreement with the accepted geological time scale are selectively published in preference to those results that are not in agreement.
The geological time scale and an age for the Earth of 4.5 b.y.
Since the lead in meteorites can no longer be ascribed to uranium/thorium decay, it may also be taken to represent primordial lead.
Therefore, since the lead isotope ratios for the majority of meteorites are the same as present day common lead ratios and may also be assumed to represent primordial lead, the billion year age chronology disappears.
rely heavily on the uranium/thorium/lead radiometric dating methods.